MUTATIONS AT THE SPINDLY LOCUS OF ARABIDOPSIS ALTER GIBBERELLIN SIGNAL-TRANSDUCTION

Three independent recessive mutations at the SPINDLY (SPY) locus of Ar abidopsis confer resistance to the gibberellin (GA) biosynthesis inhib itor paclobutrazol. Relative to wild type, spy mutants exhibit longer hypocotyls, leaves that are a lighter green color, increased stem elon gation, early flowering, parthenocarpy, and partial male sterility. Al l of these phenotypes are also observed when wild-type Arabidopsis pla nts are repeatedly treated with gibberellin A3 (GA3). The spy-1 allele is partially epistatic to the ga1-2 mutation, which causes GA deficie ncy. in addition, the spy-1 mutation can simultaneously suppress the e ffects of the ga1-2 mutation and paclobutrazol treatment, which inhibi t different steps in the GA biosynthesis pathway. This observation sug gests that spy-1 activates a basal level of GA signal transduction tha t is independent of GA. Furthermore, results from GA3 dose-response ex periments suggest that GA3 and spy-1 interact in an additive manner. T hese results are consistent with models in which the SPY gene product regulates a portion of the GA signal transduction pathway.